I have narrowed down my problem to exhaust fan, last test was to close vacuum switch and fireplace lights. Fan just hums, never comes on. I have found 288-125a replacement assembly and looked at photos. Can just the bottom motor/winding assembly be pulled replaced from underneath? Or second, can the rotor housing assembly (round) be separated from the sheet metal underneath, or will I need to replace the whole assembly (which looks like a lot of sheet metal to remove to get to all the fan screws). Thanks Hearthbroken